This invention relates to an image forming apparatus for forming a color image on a photosensitive recording medium, and more particularly to an image forming apparatus having at least two color separation filters which provide different half-widths in wavelengths (spectrum) of lights transmitted therethrough.
There has been conventionally utilized an image forming apparatus in which mask members or intermediate sheets for forming three primary color images such as red, green and blue images are beforehand produced by a monochromatic printer and then a photosensitive recording medium is exposed to light through the mask members or intermediate sheets to thereby forming a color latent image on the photosensitive recording medium. This image forming apparatus further includes a color separation filter unit comprising a set of red, green and blue color separation filters which are used to separate red, green and blue lights from a white light, and a filter switching or selecting unit for switching one of the color separation filters to another according to the type (red, green or blue) of a mask member to be exposed to light.
In an exposure process, a white light which has been color-separated by a color separation filter is irradiated through the corresponding mask member to the photosensitive recording medium (hereinafter referred to as "photosensitive sheet") to form one of the red, green and blue color latent images. This exposing operation is repeated for forming the other color latent images, and a color image corresponding to an original image is finally formed on the photosensitive sheet.
In the conventional image forming apparatus thus constructed, two types of color separation filter units as described below are used to shorten an exposure time for which the photosensitive recording medium is exposed through the mask members, and to improve an image quality of a finally-obtained color image, respectively.
In order to shorten the exposure time, each of the color separation filters of the color separation filter unit is so designed that a half-width in wavelength (spectrum) of light transmitted therethrough is broader and thus a light-amount of the transmitted light is larger. However, in this type of color separation filters, a crosstalk is liable to occur between the neighboring different kinds of microcapsules having sensitivities to different wavelength ranges because each color separation filter provides a transmitted light having a broader half-width in spectrum.
On the other hand, in order to improve the image quality of an output color image, each of the color separation filters is so designed that the half-width in wavelength (spectrum) of the transmitted light is narrower. However, in this type of color separation filters, the exposure time must be more increased because the half-width in spectrum of the transmitted light is narrower and thus the light-amount of the light is smaller.
In the conventional image forming apparatus as described above, however, only one of the color separation filter units as described above can be individually used in the image forming apparatus in order to attain either of the above objects. That is, both of the color separation filter units as described above can not be used in combination mode or in switching mode in the conventional apparatus to attain both of the above objects. In addition, an user can not freely select one of the color separation filters as described above, that is, the right of choice is not provided to the user.